Many areas of industry use looped material bands, either as power transmission elements such as belts or as transport elements such as conveyor belts, conveyors, etc. These material bands present classically a structure and technical characteristics specifically adapted according to the intended application.
The power transmission belts are classically made from materials designed to improve their fatigue life and resist all mechanical, physical and/or chemical stress they are commonly subjected to in operation. Among the power transmission belts presently available on the market, those marketed under the name PolyChain® and manufactured out of a light and robust polyurethane compound distinguish themselves by their excellent mechanical performance and their very high fatigue resistance. Such transmission belts are in particular four times more resistant than the traditional belts, since they are reinforced with spirally wound tensile cords, for example made of carbon or Kevlar®, embedded in their thickness. They have the shape of endless sleeves manufactured under a press in a form whose diameter determines their length, these sleeves being then cut or slit according to the required width of every belt. Due to such an endless structure, without splice area, the mechanical resistance properties of such transmission belts are advantageously preserved. They nevertheless have the disadvantage that their installation on a machine, as well as their removal for replacement, requires the disassembly of the machine, or even the intervention of the manufacturer of the machine, imposing a stoppage of the machine, which is detrimental to the profitability of the production equipment. At the moment, the handling operations of such transmission belts, whether of the PolyChain® type or of any other type, having the shape of endless sleeves, show consequently to be particularly laborious, time-consuming and costly.
The reversible splice solutions commonly used in the area of conveyor belts and described in a number of publications do not show to be totally satisfactory when they are transposed as such on power transmission belts such as those described previously, which presuppose, as mentioned, a structure able to resist mechanical stress, due in particular to the high power torques to transmit and to a high rotational speed, both being markedly higher than those found in the conveying branch.
So, publication EP 2 108 860, relating to a looped material band intended for being used as a conveyor belt, provides to equip said belt with a splice area comprising two serrations to be engaged into each other, obtained by stamping, and in which the teeth are delimited by a rectangular perimeter and have different lengths so that the ends of the teeth are offset longitudinally with respect to each other. The main disadvantage of this solution, when it is implemented within the framework of a power transmission belt, is due to the fact that the shape offered for said teeth has sharp angles. Even though such a feature is very well adapted for a conveyor belt, classically made out of a material such as extruded polyurethane reinforced with longitudinal steel tensile cords, it appears that the presence of any sharp angle reduces drastically the lifetime of a transmission belt, in particular of the PolyChain® type, made of comparatively harder polyurethane and whose spirally wound tensile cords are more flexible. Furthermore, a splice area in which the ends of the teeth show a longitudinal offset requires also more connecting pins, which makes the assembly of such a splice less easy. In addition, the polyurethane used for a power transmission belt of the PolyChain® type is so hard that the classical stamping tools wear very quickly and lose their shape, and thus do not allow reproducing with a sufficient accuracy the complementary shapes of the serrations of the splice area, therefore penalizing the mechanical resistance of the splice.
Another solution, described in publication U.S. Pat. No. 3,744,095, provides to equip the ends of a transmission belt comprising longitudinal tensile cords with dado-shaped serrations intended to be assembled with threaded connecting pins. The disadvantage of such a dado cut lies not only in the presence of sharp angles on the serrations, but also in the fact that all cords are cut at the same level, aligned over the whole width of the belt, the fatigue of which is then strongly favored. Even though the dado shape of the serrations proposed by this publication is suitable in the case of longitudinal cords, it cannot be transposed to a power transmission belt, in particular of the PolyChain® type, in which the cords are wound spirally. The cuts parallel to the longitudinal edges of the belt performed when stamping the serrations imply cutting longitudinally at least one spirally wound cord, which results in reducing the fatigue life of said belt in the splice area.